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SubjectRe: [PATCH] kmemcheck: make bitfield annotations truly no-ops when disabled
Vegard Nossum kirjoitti:
> It turns out that even zero-sized struct members (int foo[0];) will affect
> the struct layout, causing us in particular to lose 4 bytes in struct sock.
>
> This patch fixes the regression in CONFIG_KMEMCHECK=n case.
>
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>

Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>

> ---
> include/linux/kmemcheck.h | 110 ++++++++++++++++++++++++---------------------
> 1 files changed, 58 insertions(+), 52 deletions(-)
>
> Andrew: Compile tested on x86_32 and x86_64, but because of my bad track
> record when it comes to brown paper bugs, can you please keep this in -mm
> for a little while? Thanks.
>
> diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h
> index e880d4c..08d7dc4 100644
> --- a/include/linux/kmemcheck.h
> +++ b/include/linux/kmemcheck.h
> @@ -36,6 +36,56 @@ int kmemcheck_hide_addr(unsigned long address);
>
> bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size);
>
> +/*
> + * Bitfield annotations
> + *
> + * How to use: If you have a struct using bitfields, for example
> + *
> + * struct a {
> + * int x:8, y:8;
> + * };
> + *
> + * then this should be rewritten as
> + *
> + * struct a {
> + * kmemcheck_bitfield_begin(flags);
> + * int x:8, y:8;
> + * kmemcheck_bitfield_end(flags);
> + * };
> + *
> + * Now the "flags_begin" and "flags_end" members may be used to refer to the
> + * beginning and end, respectively, of the bitfield (and things like
> + * &x.flags_begin is allowed). As soon as the struct is allocated, the bit-
> + * fields should be annotated:
> + *
> + * struct a *a = kmalloc(sizeof(struct a), GFP_KERNEL);
> + * kmemcheck_annotate_bitfield(a, flags);
> + */
> +#define kmemcheck_bitfield_begin(name) \
> + int name##_begin[0];
> +
> +#define kmemcheck_bitfield_end(name) \
> + int name##_end[0];
> +
> +#define kmemcheck_annotate_bitfield(ptr, name) \
> + do { \
> + int _n; \
> + \
> + if (!ptr) \
> + break; \
> + \
> + _n = (long) &((ptr)->name##_end) \
> + - (long) &((ptr)->name##_begin); \
> + MAYBE_BUILD_BUG_ON(_n < 0); \
> + \
> + kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
> + } while (0)
> +
> +#define kmemcheck_annotate_variable(var) \
> + do { \
> + kmemcheck_mark_initialized(&(var), sizeof(var)); \
> + } while (0) \
> +
> #else
> #define kmemcheck_enabled 0
>
> @@ -106,60 +156,16 @@ static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
> return true;
> }
>
> -#endif /* CONFIG_KMEMCHECK */
> -
> -/*
> - * Bitfield annotations
> - *
> - * How to use: If you have a struct using bitfields, for example
> - *
> - * struct a {
> - * int x:8, y:8;
> - * };
> - *
> - * then this should be rewritten as
> - *
> - * struct a {
> - * kmemcheck_bitfield_begin(flags);
> - * int x:8, y:8;
> - * kmemcheck_bitfield_end(flags);
> - * };
> - *
> - * Now the "flags_begin" and "flags_end" members may be used to refer to the
> - * beginning and end, respectively, of the bitfield (and things like
> - * &x.flags_begin is allowed). As soon as the struct is allocated, the bit-
> - * fields should be annotated:
> - *
> - * struct a *a = kmalloc(sizeof(struct a), GFP_KERNEL);
> - * kmemcheck_annotate_bitfield(a, flags);
> - *
> - * Note: We provide the same definitions for both kmemcheck and non-
> - * kmemcheck kernels. This makes it harder to introduce accidental errors. It
> - * is also allowed to pass NULL pointers to kmemcheck_annotate_bitfield().
> - */
> -#define kmemcheck_bitfield_begin(name) \
> - int name##_begin[0];
> -
> -#define kmemcheck_bitfield_end(name) \
> - int name##_end[0];
> +#define kmemcheck_bitfield_begin(name)
> +#define kmemcheck_bitfield_end(name)
> +#define kmemcheck_annotate_bitfield(ptr, name) \
> + do { \
> + } while (0)
>
> -#define kmemcheck_annotate_bitfield(ptr, name) \
> - do { \
> - int _n; \
> - \
> - if (!ptr) \
> - break; \
> - \
> - _n = (long) &((ptr)->name##_end) \
> - - (long) &((ptr)->name##_begin); \
> - MAYBE_BUILD_BUG_ON(_n < 0); \
> - \
> - kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
> +#define kmemcheck_annotate_variable(var) \
> + do { \
> } while (0)
>
> -#define kmemcheck_annotate_variable(var) \
> - do { \
> - kmemcheck_mark_initialized(&(var), sizeof(var)); \
> - } while (0) \
> +#endif /* CONFIG_KMEMCHECK */
>
> #endif /* LINUX_KMEMCHECK_H */



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